The causes may be physiological or psychological. Psychological impotence can often be helped by almost anything that the patient believes in; there is a very strong placebo effect.

Due to its embarrassing nature and the shame felt by sufferers, the subject was taboo for a long time, and is the subject of many urban legends. Folk remedies have long been advocated, with some being advertised widely since the 1930s. The introduction of perhaps the first pharmacologically effective remedy for impotence, sildenafil (trade name Viagra), in the 1990s caused a wave of public attention, propelled in part by the news-worthiness of stories about it and heavy advertising.

The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina. It is now mostly replaced by more precise terms.

A useful and simple way to distinguish between physiological and psychological impotence is to determine whether the patient ever has an erection. If never, the problem is likely to be physiological; if sometimes (however rarely), it is more likely to be psychological.

Duplex ultrasound is used to evaluate blood flow, venous leak, signs of atherosclerosis, and scarring or calcification of erectile tissue. Injecting prostaglandin, a hormone-like stimulator produced in the body, induces erection. Ultrasound is then used to see vascular dilation and measure penile blood pressure. Measurements are compared to those taken when the penis is flaccid.

Penile nerves function

Tests such as the bulbocavernosus reflex test are used to determine if there is sufficient nerve sensation in the penis. The physician squeezes the glans (head) of the penis, which immediately causes the anus to contract if nerve function is normal. A physician measures the latency between squeeze and contraction by observing the anal sphincter or by feeling it with a gloved finger inserted past the anus. Specific nerve tests are used in patients with suspected nerve damage as a result of diabetes or nerve disease.

Nocturnal penile tumescence (NPT)

It is normal for a man to have five to six erections during sleep, especially during rapid eye movement (REM). Their absence may indicate a problem with nerve function or blood supply in the penis. There are two methods for measuring changes in penile rigidity and circumference during nocturnal erection: snap gauge and strain gauge.

Penile biothesiometry

This test uses electromagnetic vibration to evaluate sensitivity and nerve function in the glans and shaft of the penis. A decreased perception of vibration may indicate nerve damage in the pelvic area, which can lead to impotence.

Penile erection is managed by two different mechanisms. The first one is the reflex erection, which is achieved by directly touching the penile shaft. The second is the psychogenic erection, which is achieved by erotic stimuli. The former uses the peripheral nerves and the lower parts of the spinal cord, whereas the latter uses the limbic system of the brain. In both conditions an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system leads to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy male erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply or psychological problems. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease, but can also include causation by prolonged exposure to bright light or chronic exposure to high noise levels.

Treatment depends on the cause. Testosterone therapy supplements may be used for cases due to hormonal deficiency. However, the cause is more usually lack of adequate penile blood supply as a result of damage to inner walls of blood vessels. This damage is more frequent in older men, and often associated with disease, in particular diabetes.

Treatments (with the exception of testosterone supplementation, where effective) work on a temporary basis: they enable an erection to be attained and maintained long enough for intercourse, but do not permanently improve the underlying condition.

ED can in many cases be treated by drugs taken orally, injected, or as penile suppositories. These drugs increase the efficacy of NO, which dilates the blood vessels of corpora cavernosa. When oral drugs or suppositories fail, injections (e.g. of apomorphine) into the erectile tissue of the penile shaft may work.

When pharmacological methods fail, a purpose-designed external vacuum pump can be used to attain erection, with a separate compression ring fitted to the penis to maintain it. These pumps should be distinguished from other "penis pumps" (supplied without compression rings) which, rather than being used for temporary treatment of impotence, are claimed to increase penis length if used frequently, or vibrate as an aid to masturbation.

More drastically, inflatable or rigid penile implants may be fitted surgically. Implants are irreversible and costly.

All these mechanical methods are based on simple principles of hydraulics and mechanics and are quite reliable, but have their disadvantages.

In a few cases there is a vascular problem which can be treated surgically.

An external vacuum pump will produce an engorged penis with success approaching 90%; a penis ring will maintain this state, although it should be removed after not more than 30 minutes. The erection is not as rigid or hard as a natural erection; drugs or injections, when they work, may be preferable. Various studies show the degree of satisfaction of users and their partners to be vary variable, even when drugs and injections do not work; in one study, about 20% of men who tried a (high-priced) pump decided to proceed to purchase one. Other studies show higher percentages of satisfied users.

In some cases frequent use of a vacuum pump can eventually improve the degree of erection attainable without use of the pump. Claims of cheap "penis pumps" to permanently increase maximum penis size should be viewed with caution, however.

Some vacuum pumps are sold at a higher price with 100% refund within 90 days to dissatisfied users, with a somewhat lower price with 50% refund guarantee (Osbon Erecaid, [1]). This pump is supported by medical insurance schemes, including the UK's NHS and US Medicare and private insurers. The better-known pumps sell for prices of around 200 GBP/400 USD (2006). There is at least one vacuum pump with rings which sells for around one-fifth of this price (Noogleberry, [2]). Specific devices are mentioned for information only; mention should not be taken as endorsement.

The experimental drug Bremelanotide (formerly PT-141) does not act on the vascular system like the former compounds but increases sexual desire and drive in male as well as female. It is applied as a nasal spray. Bremelanotide works by activating melanocortinreceptors in the brain. It is awaiting FDA approval.

Ginseng

A double-blind study appears to show evidence that ginseng is better than placebo: see the ginseng article for links and more details.

Enzyte

Enzyte is a supplement that claims to increase the male libido or frequency of erections of the penis. It has been advertised by saturation coverage on television channels in the US. However, the Center for Science in the Public Interest (CSPI) has filed a complaint with the Federal Trade Commission (FTC) about Enzyte for deceptive advertising. The effectiveness of Enzyte is in dispute. Some medical professionals in fact advise against taking Enzyte, saying that it can lead to damage.

Herbal and other alternative treatments

These are generally ineffective when tested blind, but may be useful for their psychological (placebo) effect: if a good result is expected, any highly-praised, and often expensive, treatment can be effective. Reputable drugs can also benefit from the same effect.

Modern drug therapy for ED was advanced enormously in 1983 when British physiologist Giles Brindley, Ph.D. dropped his trousers and demonstrated to a shocked American Urological Association audience his phentolamine-induced erection. The drug Brindley injected into his penis was a non-specific vasodilator, an alpha-blocking agent, and the mechanism of action was clearly corporal smooth muscle relaxation. The effect that Brindley discovered, established the fundamentals for the later development of specific, safe, orally-effective drug therapies.[3]

Argiolas, A. (1992). Oxytocin stimulation of penile erection: Pharmacology, site, and mechanism of action. In Oxytocin in maternal, sexual, and social behaviors (pp. 194-203). New York, NY: New York Academy of Sciences.

Kim, S.-C., & Park, H. S. (2006). Five Years After the Launch of Viagra in Korea: Changes in Perceptions of Erectile Dysfunction Treatment by Physicians, Patients, and the Patients' Spouses. Journal of Sexual Medicine, 3(1), pp.

Sakheim, D. K. (1985). Waking assessment of erectile potential: The validation of a laboratory procedure to aid in the differential diagnosis of psychogenic and organic impotence. Sakheim, David K : State U New York, Albany.

Wagner, T., Patrick, D., McKenna, S., & Froese, P. (1996). Cross-cultural development of a quality of life measure for men with erection difficulties. Quality of Life Research: An International Journal of Quality of Life Aspects of Treatment, Care & Rehabilitation, 5(4), pp.